Effects of prindolol on isoproterenol-induced subendocardial ischaemia in dogs with multiple chronic coronary artery occlusion.

Abstract

Multiple chronic coronary artery occlusions were produced in dogs by implantation of ameroid rings on the circumflex branches of the left and right coronary artery. Sixty-five per cent of the animals survived. Seventy-seven per cent of the remaining animals had no detectable myocardial infarction. Myocardial blood flow distribution was studied 4 weeks after operation using the tracer microsphere technique. During control conditions myocardial blood flow was homogeneously distributed within the left ventricle. In one group of dogs, regional dilatory capacity was tested by intravenous infusion of dipyridamole. Four compartments of myocardial blood flow were found. The collateral dependent subendocardium with 114 ml/min-100 g-1 was the lowest perfusion rate. In another group of dogs myocardial blood flow distribution was examined during isoproterenol infusion and after beta-blockade with prindolol during continuous isoproterenol infusion. During isoproterenol infusion, a nonhomogeneous blood flow pattern was found when the heart rate increased to 200/min together with a slight fall in diastolic perfusion pressure. Under these conditions, the flow to the collateral dependent subendocardium was severely diminished, while the flow to the areas perfused by normal coronary arteries increased, reflecting compensatory vasodilation. After beta-blockade with prindolol 0.1 mg/kg, the myocardial blood flow distribution was also nonhomogeneous but in the opposite direction: the collateral dependent subendocardium was now the best perfused compartment. The flow to the areas perfused by normal coronary arteries decreased due to the reduced oxygen requirements, while the collateral dependent subendocardium remained maximally dilated. This phenomenon was explained as a postischaemic reactive hyperaemic response to the isoproterenol-induced ischaemia in the collateral dependent subendocardium.